The present invention relates to a method for operating a machine that processes printing substrates in sheet form, in particular, a printing press, including a delivery device which contains a drive for conveying the substrate sheets and at least one opening through which the substrate sheets can be conveyed from the inside of the delivery device to an externally accessible region, and further including a control device which controls at least one closing device for opening or closing the opening and which is operatively connected to the drive of the delivery device. Moreover, the present invention relates to a device for carrying out the specified method mentioned.
Sheet-fed rotary printing presses are essentially composed of three units: the feeder for feeding substrate sheets into the printing press, the printing units for printing on the substrate sheets, and the delivery device for outputting the printed substrate sheets. In this context, the substrate sheets is usually deposited on a pile in the delivery device which, when it reaches a certain height, it removed so that a new delivery pile is built up. Therefore, a central task of the delivery device is to convey the substrate sheets from the last printing unit or a drying unit or varnishing unit to the delivery pile. For this purpose, most delivery devices have movable gripper bridges which convey the substrate sheets and deposit them on the delivery pile when reaching the pile. Therefore, the delivery device should have an opening in the region above the delivery pile through which the substrate sheets can get from the inside of the delivery device to the delivery pile. The delivery pile, in turn, must be accessible to the operating personnel because the pile needs to be regularly changed. Therefore, there is a risk of the operating personnel bringing the head, torso or limbs into contact with dangerous parts, in particular with the gripper bridges, inside the delivery device through the opening. Therefore, there are safety regulations, also on the part of the workers' compensation associations, which are intended to contribute to the prevention of potential injuries in the region of the delivery devices.
Currently, the hazard is sought to be prevented primarily by generating audible and visual warning signals during the starting of the delivery device and the printing press. In this context, however, there is always the risk that the warning signals are not heard or seen, as a result of which the risk to the operating personnel continues.
A method for increasing the operational safety in the region of the delivery device of a printing press is known from German Patent Application No. DE 199 25 065 A1. This patent application is based on the idea of monitoring the externally accessible free space below an outlet opening of the delivery device in such a manner that this free space does not exceed a certain predetermined amount. In this context, this amount has to be kept so small that the operating personnel cannot get into contact with dangerous moving parts of the delivery device during the operation thereof. Thus, in particular, the operating personnel is prevented from reaching into operating gripper bridges. In this context, the monitoring of the free space takes place in such a manner that in the region below the opening of the delivery device, a movable pile board is located on which are deposited printed sheets comimg from inside the delivery device through the opening. The more sheets are deposited, the higher the pile, requiring the movable pile board to be correspondingly lowered. In this context, however, the pile board, while controlled by a monitoring sensor, is lowered only so far that the free space between the top edge of the pile of printed sheets and the opening of the delivery device does not exceed the prescribed safety level. As soon as the amount of free space that is only just safe is determined to be exceeded, the main drive of the printing press, which also drives the delivery device via gear wheels or shafts, is stopped. Restarting the printing presses along with the delivery device is only possible if the free space has in the meantime been reduced to the prescribed amount. In one embodiment of German Patent Application No. DE 199 25 065 A1, provision is also made for a roller shutter to be mounted below the opening of the delivery device in order to limit the free space. Such a roller shutter is retracted to the height of the maximum admissible free space and thus, while in the closed state, allows the printing press to be put into operation again along with the delivery device even if the top edge of the pile is too far away from the opening.
The design of a safety system on the delivery device known from German Patent Application No. DE 199 25 065 A1 offers far-reaching protection of operating personnel from injury from rotating parts of the delivery device. However, this design approach has the crucial disadvantage that the delivery device and the printing press are always stopped when the maximum admissible free space is exceeded. After that, the printing press must then be restarted in the prescribed manner. However, stopping the whole machine is very unpopular with the operating personnel due to the corresponding expenditure of time.